Polyesters have excellent mechanical, physical, and chemical performance, and thus have been widely used for fibers, films, and other formed products. Among them, in recent years, attention has been paid to polytrimethylene terephthalate fibers for their soft texture, excellent elastic recovery, dyeability, and like characteristics that are not seen in conventional polyester fibers, such as polyethylene terephthalate fibers. Accordingly, they have been widely applied as fibers for carpets, brushes, and garments.
When synthetic fibers using polyesters including such polytrimethylene terephthalate, nylon, and the like are used for garment applications, generally, titanium dioxide is added as a delustering agent to suppress the luster of fibers. However, in the case where titanium dioxide is added to a polyester, due to the surface activity of inorganic particulate titanium dioxide, the polyester polymer is decomposed, resulting in problems such as a decrease in molecular weight. Then, single-fiber breakage occurs during spinning, for example, causing a decrease in the stability of the fiber production process. Other known problems include fluffing, the occurrence of variations in hue and cloth texture, and the like, resulting in the deterioration of the quality of the product. In particular, as compared with typical polyesters such as polyethylene terephthalate, polytrimethylene terephthalate has lower thermal stability. Accordingly, the adverse effects on the fiber production process caused by the presence of titanium dioxide inorganic particles are likely to be more prominent.
Methods for solving these problems with the production of polytrimethylene terephthalate fibers and the fiber quality have been proposed, including a method in which a removal operation, such as centrifugation or filtration, is performed to reduce aggregates of titanium oxide (see, e.g., PTL 1), a method in which a pre-prepared masterbatch of tributylene terephthalate and titanium dioxide is dispersed in polytrimethylene terephthalate (see, e.g., PTL 2), and the like. Use of these methods can certainly reduce aggregates of titanium dioxide and the like contained in a polytrimethylene terephthalate composition, and filter clogging during formation is reduced, leading to the stabilization of the fiber production process. However, in the production of fibers having small single-fiber fineness, the methods have yet been at an insufficient level in terms of quality, such as yarn breakage and fluffing.
In addition, as a method for increasing the crystallization exothermic peak top temperature of a polytrimethylene terephthalate composition in order to improve the polymer melt retention stability, a method in which an epoxy-group-containing polystyrene is added to polytrimethylene terephthalate has been proposed (see, e.g., PTL 3). However, in this method, the addition of polystyrene destabilizes the fiber production process. Further, in the case where dyeing is performed in a subsequent step, the addition also causes non-uniform dyeing of a cloth, etc. As another method for improving the thermal stability of polytrimethylene terephthalate, a method in which a phosphorus compound is added to polytrimethylene terephthalate to enhance the thermal stability has been proposed (see, e.g., PTL 4). According to this method, the thermal stability of polytrimethylene terephthalate is certainly improved, leading to the stabilization of the fiber production process. However, its improving effect has yet been insufficient.